Recently, in semiconductor integrated circuits, the device size have been scale down and the integration has been improved, and micro processing has been required. In addition, the device structure has been complex and three-dimensional. The scale down has been accomplished by the improvement of micro processing technique in the manufacturing process of a semiconductor device, particularly high resolution in photolithography process which transfer a circuit pattern to photosensitive organic film (photo resist) coated on a silicon wafer. In the photolithography process, techniques of exposure by using a light source of shorter wavelength have been developed. A method of compensating the deficiency of the depth of focus to assure the resolution without defocus of a micro pattern by reducing unevenness in the device structure as possible has been attempted.
As a method of planarizing the unevenness in the device structure, the CMP method, to which mirror surface processing of a silicon wafer was applied, has been used. An apparatus for generally using in the CMP method is shown by reference to FIG. 1. The CMP apparatus used in the CMP method is provided with a polishing platen 2 for supporting a polishing pad 1 and with a supporting stand (polishing head) 5 for supporting a material to be polished 4 (such as a semiconductor wafer). The polishing platen 2 and the supporting stand 5 are arranged such that the polished pad 1 and the material to be polished 4, both of which are supported by them, are opposed to each other, and the polishing platen and the supporting stand are constituted to be capable of rotating around rotating shafts 6 and 7. The material to be polished 4 is stuck on the supporting stand 5 which is provided with a pressing mechanism for pushing the material to be polished 4 onto the polishing pad 1 at the time of polishing (not indicated). Abrasive (slurry) 3-feeding mechanism 8 is to feed an abrasive suspension having abrasive grains such as silica particles dispersed in an alkali solution to the polishing pad 1 on the polishing platen 2. In addition, the CMP apparatus comprises dresser having abrasive grains of diamond electrodeposited or melt bonded thereon to dress the surface of the polishing pad (not indicated).
As an example of the method, there is a method of dressing the polishing pad by dresser, rotating the shafts 6 and 7, pushing the wafer 4 onto the polishing pad 1 by the pressing mechanism while feeding an abrasive slurry from the abrasive slurry-feeding mechanism 8 to the center portion of the polishing pad to polishing the wafer. In the CMP method, micro scratches on the layer to be polished such as the inter layer dielectrics of the wafer, the dispersion of the abrasive rate and poor uniformity of the abrasive amount within the surface of a silicon wafer are problem.
In order to restrain the formation of the micro scratches, it is necessary that abrasive dust of the polishing pad and diamond of the dresser formed during dressing of the polishing pad, inter layer dielectrics, abrasive dust of the wafer and used abrasive slurry (collectively, abrasive waste) are discharged to the exterior of the polishing pad. In the conventional CMP apparatus, the abrasive waste is discharged by continuously feeding the abrasive slurry to the center portion of the polishing pad in a sufficient amount. In case of forming a dressed layer on the polishing pad by dressing and then polishing the wafer while feeding the abrasive slurry described above, the abrasive slurry is pushed out by centrifugal force from the rotation of the polishing pad and by pushing the wafer onto the polishing pad. Therefore, the abrasive slurry is almost discharged to the exterior of the polishing pad without concerning the polishing to consume excess abrasive slurry, which is expensive.
In order to dissolve the problems, various attempts have been made in the polishing method to improve the abrasive properties of the material to be polished. Among them, there have been various attempts with respect with grooves for remaining abrasive slurry on the polishing surface and discharging it.
In Japanese Patent No. 2647046, a polishing pad comprising grooves for flowing abrasive formed in the inner portion and the outer portion of the surface of the polishing pad, and a plurality of pores for retaining the abrasive formed on the surface of the polishing pad other than the portion that the grooves are formed, is disclosed. As one embodiment of the polishing pad, the polishing pad comprising lattice pattern groove formed in the center portion and the peripheral portion of the surface of the polishing pad, and pores formed in a portion between center portion and the peripheral portion, is described in FIG. 1. The pores are formed in broad area at once by using punches arranged in a line or a few lines. It is difficult to form the pores by using a processing apparatus generally used for that purpose. The technical effects of reducing the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not particularly disclosed. The term “unusual retainment” used herein means that the retainment of the abrasive slurry is in largely non-uniform state on the polishing surface of the polishing pad, which has a bad effect on polishing a material to be polished.
In Japanese Patent Kokai Publication No. 249710/1998, a polishing pad comprising grooves formed such that the groove shape geometrically having a center is eccentric to the polishing pad. It is described to dissolve a problem of transferring the groove shape to a silicon wafer processed to degrade the uniformity by the eccentricity of concentric circular groove to the polishing pad. However, it is difficult to prevent the abrasive rate in the center portion of the wafer from degrading. In addition, the technical effects of reducing of the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not particularly disclosed.
In Japanese Patent Kokai Publication No. 70463/1999, a polishing pad comprising a first zone having plural concentric circular grooves and a second zone having a second pitch. It is described that the polishing pad has two zones having a different groove pitch to improve the uniformity of the polishing. However, the technical effects of reducing of the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not particularly disclosed, and it is difficult to improve the uniformity of the polishing.
In Japanese Patent Kokai Publication No. 198061/2000, a polishing pad comprising plural loop grooves and plural stream-lined grooves is disclosed. In the polishing pad, it is attempted to positively control the flow of the abrasive slurry by forming the grooves into the stream-lined shape. However, in the polishing pad, it is problem that the abrasive slurry necessary to polishing flows out along the stream-lined grooves. In addition, the technical effects of reducing of the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not particularly disclosed, and the uniformity of the polishing is not sufficiently obtained.
In Japanese Patent Kokai Publication No. 224950/2002, a polishing pad comprising grooves having arc shaped bottom to prevent the abrasive slurry from stagnating. In the polishing pad, it is attempted to control the flow of the abrasive slurry smoothly by forming the grooves into the arc bottom shape. In the polishing pad, the shape of the groove and the surface roughness thereof are considered. However, it is different from the present invention in view that the polishing surface material is round graphite cast iron. In addition, it is different from the present invention in view that the material to be polished is bare wafer or glass substrate. Moreover, the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not discussed in case of using porous material as the polishing layer as described in the present invention.
In Japanese Patent Kokai Publication No. 9156/2004, a polishing pad comprising grooves, of which the inner surface has a surface roughness of not more than 20 μm, on the polishing surface. In the polishing pad, the surface roughness of the inner surface of the groove is considered. The surface roughness of the groove is obtained for the groove formed by cutting the polishing surface material or molding it in a mold. It has been found from an additional test by the present inventors that it is difficult for the inner surface of the groove to have the surface roughness of not more than 20 μm in case of forming the groove on the pore material by the above method. Therefore, a main object of the invention is the select of the polishing layer material rather than a method of forming grooves, which is different from the present invention. In addition, the unusual retainment of the abrasive slurry based on the balance between feeding and discharging the abrasive slurry are not discussed in case of using porous material as the polishing layer as described in the present invention.
In order to dissolve the problems, a polishing pad for processing semiconductor device that concentric circular grooves having right-angle edge are formed at the upper edge portion of the groove and groove processing tool are disclosed in Japanese Patent Kokai Publication Nos. 181649/2001 and 184730/2002, and a fine groove processing machine, processing tool and method of processing for forming concentric circular grooves or lattice pattern groove on semiconductor polishing pad for CMP processing are disclosed in Japanese Patent Kokai Publication No. 11630/2002.
In the polishing pad disclosed in Japanese Patent Kokai Publication. Nos. 181649/2001 and 184730/2002, it is easy to control the flow of the abrasive slurry between the device surface to be polished and the upper surface of the pad by forming concentric circular grooves having right-angle edges at the upper corner portion in cross section and adjusting the width, depth and pitch of the groove to specified ranges, and it is expected that hydroplaning is restrained and the soft metal surface of the device is effectively planarized by the CMP processing method. However, the cross section shape of the groove is not stable, and the flowability of the abrasive slurry varies every pad. Therefore, stable abrasive properties are not sufficiently obtained.
In the polishing pad comprising fine grooves formed by the groove processing tool disclosed in Japanese Patent Kokai Publication No. 11630/2002, the cross section shape of the groove is not stable, and the flowability of the abrasive slurry varies every pad. Therefore, scratches are easily formed, and stable abrasive properties are not sufficiently obtained.
In the above polishing pad disclosed in Japanese Patent Kokai Publications Nos. 181649/2001, 184730/2002 and 11630/2002, edges at the corner portion in cross section of the groove is right-angle by specifying the shape of the cutting edge of the groove processing tool, thereby it is attempted to restrain the occurrence of dulled edge and burr on the wall surface of the groove. Stable abrasive properties are not sufficiently obtained only by specifying the shape of the cutting edge of the groove processing tool.